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[209.132.183.28]) by mx.google.com with ESMTPS id y35si1285847qty.173.2019.03.12.00.15.32 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 12 Mar 2019 00:15:32 -0700 (PDT) Received-SPF: pass (google.com: domain of jasowang@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of jasowang@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=jasowang@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id E75A2723D9; Tue, 12 Mar 2019 07:15:31 +0000 (UTC) Received: from [10.72.12.17] (ovpn-12-17.pek2.redhat.com [10.72.12.17]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0731660A9A; Tue, 12 Mar 2019 07:15:23 +0000 (UTC) Subject: Re: [RFC PATCH V2 5/5] vhost: access vq metadata through kernel virtual address To: "Michael S. Tsirkin" Cc: Andrea Arcangeli , kvm@vger.kernel.org, virtualization@lists.linux-foundation.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, peterx@redhat.com, linux-mm@kvack.org, Jerome Glisse References: <1551856692-3384-1-git-send-email-jasowang@redhat.com> <1551856692-3384-6-git-send-email-jasowang@redhat.com> <20190307103503-mutt-send-email-mst@kernel.org> <20190307124700-mutt-send-email-mst@kernel.org> <20190307191622.GP23850@redhat.com> <20190308194845.GC26923@redhat.com> <8b68a2a0-907a-15f5-a07f-fc5b53d7ea19@redhat.com> <20190311084525-mutt-send-email-mst@kernel.org> <20190311234956-mutt-send-email-mst@kernel.org> From: Jason Wang Message-ID: <3b00dc4a-b1b7-aa3f-c4ba-515138e4d6dd@redhat.com> Date: Tue, 12 Mar 2019 15:15:22 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 In-Reply-To: <20190311234956-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Tue, 12 Mar 2019 07:15:32 +0000 (UTC) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 2019/3/12 上午11:50, Michael S. Tsirkin wrote: >>>> Using direct mapping (I >>>> guess kernel will always try hugepage for that?) should be better and we can >>>> even use it for the data transfer not only for the metadata. >>>> >>>> Thanks >>> We can't really. The big issue is get user pages. Doing that on data >>> path will be slower than copyXuser. >> I meant if we can find a way to avoid doing gup in datapath. E.g vhost >> maintain a range tree and add or remove ranges through MMU notifier. Then in >> datapath, if we find the range, then use direct mapping otherwise >> copy_to_user(). >> >> Thanks > We can try. But I'm not sure there's any reason to think there's any > locality there. > Ok, but what kind of locality do you mean here? Thanks